In vertical drill rigs it has long been the established practice to utilize a drive kelly having a drilling tool supported from its lower end, and at some point along its vertical length the drive kelly passes through an opening in a rotary table which is drivingly rotated for imparting a rotating movement through the kelly to the drilling tool. If the hole being drilled is very shallow, or the formation is very soft, the vertical drive of the drilling tool can be accomplished by gravity along. That is, the combined weight of the drilling tool and the drive kelly are sufficient to drive the drilling tool downward at the necessary rate of travel.
In many instances, however, when the depth of the hole becomes greater, or the formation being cut is relatively hard, then the mere weight of the equipment is no longer sufficient to accomplish the drilling action at a satisfactory rate of speed. It then becomes necessary, or at least economically advantageous, to accelerate the downward travel of the drilling tool by "crowding" the kelly.
It has heretofore been known to utilize a crowd mechanism having a positive drive, such that a powered downward movement of the crown mechanism is fully and directly imparted to the drive kelly and hence to the drilling tool. Another known type of crowd mechanism is the friction crowd in which another member is placed in longitudinal sliding engagement with the drive kelly, and is moved downwardly in order to at least partially transmit its downward movements through the drive kelly to the drilling tool.
In drilling relatively deep holes such as 100 feet or more it is generally the practice to utilize either a double kelly or a triple kelly. Thus the kelly is provided with multiple sections which have a longitudinally collapsed position in which they are concentrically arranged, or which may be longitudinally extended so that each section overlaps a small portion of the length of the next.
It will be evident that the arrangement of the vertical drill rig including its rotary table, drive kelly, and crowd mechanism, becomes a rather complex problem when an effort is made to achieve maximum drilling speeds, maximum depth of hole to be cut, and at the same time maintaining the original cost of equipment as well as the maintenance expense thereof at minimum levels.
It is, therefore, the purpose and object of the present invention to provide a kelly crowd for a vertical drill rig which has advantages not obtainable with previously known types of crowd mechanism. A further object of the invention is to modify a vertical drill rig in an appropriate manner to incorporate an improved crowd mechanism therein.